1. Field of the Invention
The invention pertains to a cyclical thermal management system for maintaining a high altitude platform within a particular altitude range. More particularly, the invention pertains to a long duration, energy efficient, cyclical thermal management system for maintaining high altitude vehicles at a particular altitude and pitch attitude by cyclically manipulating the temperature of one or more of the lifting gases or ballast components in the high altitude platform in response to the effects of diurnal heating and nocturnal cooling cycles and seasonal variations in daylight cycles, the solar flux, and the albedo flux from earth.
The novel cyclical system of the invention responds to the sun""s cyclical heating and nocturnal cooling of lifting gases in geostationary high altitude platforms by a corresponding cyclical regulation or manipulation of the temperature of the lifting gas or ballast components and hence buoyancy of the platform to maintain the platform within a particular altitude range and at a particular pitch attitude. The cyclical thermal regulation or manipulation of the lifting gas or ballast components involves not only a daily cycle responsive to the heating and cooling of the lifting gas by the sun, but also the seasonal cyclical pattern of the climate of the particular geostationary location above the surface of the earth.
The cyclical regulation or manipulation of the lifting gas is achieved by processing energy by utilizing cyclical heating and cooling physical actions and chemical reactions alone or together with the chemical or mechanical processing of a portion of the lifting gas or ballast components to maintain a particular altitude or altitude range as well as the potential for future replenishment and storage of lifting gas in a non buoyant ballast compound. The cyclical processing of heat alone or together with the processing of the lifting gas or ballast components is the basic part of the novel active system of the invention.
Buoyancy control in accordance with the best mode of the invention is achieved by a combination of active and passive systems wherein the passive system is designed to reduce the volume of material processed or energy transfer manipulations required from the active system. The combination of a cyclical active system with the passive system also reduces energy and power requirements for maintaining a geostatic position. The related prior art has used the term xe2x80x9cgeostationaryxe2x80x9d to describe a predetermined horizontal position but not maintaining a predetermined altitude and pitch attitude. As used herein the term xe2x80x9cgeostaticxe2x80x9d will be used to refer not only to a predetermined horizontal position but also a predetermined altitude and pitch attitude of the novel high altitude platform.
The cyclical active system involves a diurnal as well as a seasonal manipulation of the lifting gases or ballast components by either the conversion of a portion of the lifting gas into a material of less buoyancy as ballast and then later reconverting all or a portion of the material of less buoyancy back into a lifting gas or by an increase in the weight of the ballast component and then later decreasing the weight of the ballast component. For example, hydrogen and oxygen can be processed on a daily basis to provide physical and chemical exothermic reactions during the night to heat the lifting gas at night and provide water. Water produced at night is stored in a water ballonet where in freezing it stores energy in the form of latent and sensible heat which is used to help cool the lifting gas in the early morning before the water is reprocessed during the day to store the sun""s energy for use in generating heat during the next night to control buoyancy. For seasonal variation water can be disassociated into hydrogen which is used as additional lifting gas during the winter and oxygen can be expelled into the stratosphere. In the summer oxygen can be reacquired from the stratosphere and recombined with the hydrogen lifting gas to produce water to reduce the volume of the lifting gases, increase the weight of the ballast components and increase the volume of recyclable energy storage materials available for heating and cooling processes to heat and cool the lifting gas.
The cyclical active system also involves a diurnal and seasonal manipulation of the temperature of the lifting gas utilizing heating and cooling physical processes and chemical reactions of the lifting gas or ballast component. The cyclical active system also includes a system for replenishing lifting gas lost through diffusion or the cyclical conversion and reconversion process or as may be required by seasonal variations for a particular geostatic location.
The cyclical active system also provides for the mechanical manipulation and regulation of the lift properties of the lifting gas by utilizing lifting gas circulation fans, shutters or louvers for shielding the lifting gas and variable heat conductance systems. The cyclical active system preferably also includes separately inflatable and deflatable layers for selectively varying the heat transmitted through the skin in relation to its relative position to the sun. These active systems are combined with various passive systems such as utilizing materials having desirable convective and radiative properties for various components including the utilization of heat and radiation reflective layers, a white coating on upper surfaces, no coating on the lower surfaces and materials having desirable convective and radiative properties for various components to reduce the volume of materials or the number of heat transfer manipulations required from the active system to maintain a geostatic position.
2. Description Of Related Prior Art Including Information Disclosed Under 37 C.F.R. 1.97 And 37 C.F.R. 1.98
Typically high altitude platforms are specialized types of balloons, dirigibles and lightweight platforms that are maintained aloft with a buoyant gas. These specialized prior art stratospheric platforms have remained aloft only for short durations which is typically a few days and at best a few weeks. For purposes of greater utility such platforms need to be maintained at a predetermined position which requires engines or other propulsion systems to maintain the high altitude platform over a predetermined location on the earth as stratospheric winds are encountered.
Prior art platforms referred to as geostationary were not geostatic due to the extreme temperature variations between the day and night at high altitude which caused the heating and expansion of the lifting gas during the day resulting in altitude gain, increased skin pressure and increased rates of diffusion of the lifting gas through the skin as well as possible failure of the skin material. The problem of increasing altitude during the day if not corrected in the prior art by venting or engine power is cumulative since each increase in altitude results in further expansion of the lifting gas and further lift and further skin pressure due to the decreasing density of the ambient air at higher altitudes. At night the nocturnal cooling of the lifting gas results in decreased volume and pressure and decreased altitude which could cause the platform to crash to the earth.
The conventional prior art solutions to the diurnal heating and nocturnal cooling cycles included venting a portion of the lifting gas during the day to reduce lift in an effort to maintain altitude and the integrity of the skin and a dropping of ballast at night to maintain altitude. This process of venting and dropping of ballast was for a flight duration limited by the volume of lifting gas and ballast. Another conventional prior art solution is the utilization of superpressurization to maintain altitude. The superpressurization solution required a balloon to maintain a constant volume with high internal pressures of 15,000 to 20,000 p.s.i. which put additional stress on the skin material and components that hold the skin together as discussed in Rand, et al. U.S. Pat. No. 5,104,059.
The conventional prior art also could rely upon engines, elevators and wings to divert power to maintain a geostationary position as well as a particular altitude but at the expense of pitch attitude and large amounts of energy. The sacrifice of pitch attitude sacrifices utility due to the resulting inability to control the footprint or field of vision from the platform. The additional problem of sacrificing energy results in a sacrifice of flight duration. The problem with these prior art solutions is the geostatic position of the platform is limited by the amount of energy the platform can carry, store or obtain from the outside environment which is typically sunlight. The more power required to maintain position, altitude and pitch the shorter the flight duration.
The invention unlike the prior art maintains a geostatic position by cyclically processing temperature, lifting gases and ballast weight in response to the diurnal cycles and seasonal variations and when necessary replaces lifting gases lost through diffusion or conversion by varying the chemical composition of the lifting gas and/or ballast. The invention provides for the thermal treatment of the lifting gas utilizing solar energy to maintain a geostatic position and to control skin pressure and lifting gas density during the daily heating and nocturnal cooling cycles as well as seasonal variations to provide a long duration high altitude platform. The invention provides for not only an active system for cyclically manipulating the temperature of lifting gas and the chemical nature of the lifting gas or ballast utilizing solar energy but also provides for a passive system which cooperates with the active system to minimize the magnitude of the manipulations of the active system to maintain a geostatic position.
The related art is best described as geostationary high altitude long duration lighter-than-air platforms. High altitude refers to platforms capable of maintaining an altitude of 50,000 to 120,000 feet for prolonged periods of time and that are capable of maintaining a geostationary position with respect to a predetermined geographic area. Due to the different ambient temperature, pressure and atmospheric conditions in the stratosphere as opposed to the troposphere much of the prior art pertaining to dirigibles and balloons operating in the troposphere is not applicable to geostationary high altitude long duration lighter-than-air platforms.
The related high altitude long duration prior art recognizes the importance of staying aloft for prolonged periods of time in a predetermined geographic position. The geographic position is generally defined in terms of a horizontal position over a predetermined location and not in terms of a cyclical, thermal management system for maintaining both horizontal position over a predetermined location and altitude as well as the pitch attitude and pitch angle of the high altitude platform. Wurst, et al. U.S. Pat. No. 5,518,205 provides a high altitude lighter-than-air vehicle that maneuvers during daylight hours to capture as much solar energy as possible during the day to operate the propellers, avionics and a gondola shifting mechanism. Excess energy is stored as electricity in batteries with the preferred method of energy storage being electrolysis or the conversion of water to hydrogen and oxygen gases that are stored in towed pontoons which are recombined into water at night to generate electricity at night. In Wurst, et al. U.S. Pat. No. 5,518,205 altitude control, trim and pitch angle control is provided by a combination of the forward wing, rearward wing and propellers. As a result Wurst, et al. U.S. Pat. No. 5,518,205 does not have a cyclical thermal management system to compensate for the daily heating and expansion of the lifting gas and the nocturnal cooling and resulting decreased lift and contraction of the lifting gas. Wurst, et al. U.S. Pat. No. 5,518,205 utilizes the typical prior art altitude, pitch angle:and trim control management by utilizing the forward wing, rearward wing and propellers.
Related high altitude long duration lighter-than-air platforms having a buoyancy control system for compensating for loss of lift due to nocturnal cooling is Schiff, et al. U.S. Pat. No. 3,174,705. The lifting gas density maintaining device in Schiff, et al. U.S. Pat. No. 3,174,705 is a microwave electromagnetic radiation absorbing device for absorbing beamed microwave electromagnetic radiation to raise the temperature of the lifting gas at night to compensate for the nightly cooling and resulting decreased lift and contraction of the lifting gas. Schiff, et al. U.S. Pat. No. 3,174,705 does not provide a mechanism for reducing lift during the daylight hours to maintain altitude and pitch attitude nor does Schiff, et al. U.S. Pat. No. 3,174,705 provide for reducing thermal stress on the skin or the replenishment of lifting gas lost by diffusion through the skin of the high altitude platform.; Schiff, et al. U.S. Pat. No. 3,174,705 as a result does not provide a cyclical thermal management system to compensate for daytime heating with seasonal variation or the replenishment of lost lift resulting from the loss of lifting gas for long duration applications. Schiff, et al. U.S. Pat. No. 3,174,705 also does not chemically process either ballast or lifting gas to reduce skin stress and to compensate for diurnal heating and nocturnal cooling.
Nakada U.S. Pat. No. 5,348,254 pertains to a high altitude long duration lighter-than-air platform which utilizes solar power during the day but then burns hydrogen lifting gas at night and replaces the loss of lift by utilizing exhaust heat from the engine and recovering water at night. Like Schiff, et al. U.S. Pat. No. 3,174,705, Nakada U.S. Pat. No. 5,348,254 does not have a cyclical thermal management system for reducing skin stress during the day and maintaining a particular altitude during the day. Nakada U.S. Pat. No. 5,348,254 also does not have a recyclable cyclical thermal management system to cyclically manage the lifting properties of the lifting gas during both the daytime heating and the night time cooling cycles and for the replenishment of lifting gas lost through diffusion during the day or lifting gas that is burned during the night.
Kokai No. 54-35995 pertains to a high altitude balloon carrying water which at altitude is converted by electrolysis into hydrogen and oxygen using a solar cell. The hydrogen is used to increase lift as the oxygen is discarded. This prior art increases buoyancy but does not cyclically process ballast and lifting gas to reduce skin stress and to compensate for diurnal heating and nocturnal cooling to provide a cyclical thermal management system to compensate for both daytime heating, nighttime cooling and seasonal variations to provide for a long duration high altitude thermal management system.
Other high altitude long duration related art includes Stark U.S. Pat. No. 4,364,532 which circulates cool ambient air around solar cells for cooling to increase the efficiency of the solar cell; Eshoo U.S. Pat. No. 4,262,864 which has opaque and transparent skin surface sides which are alternatively oriented toward the sun for controlling ascent and descent; and Tockert U.S. Pat. No. 4,986,494 which recognizes the high altitude problem caused by diurnal heating and the necessity of protecting the envelope skin from rupturing by the venting of the lifting gas and the nocturnal cooling and decreasing lift and the necessity of dropping ballast to maintain altitude. Tockert U.S. Pat. No. 4,986,494 solves these problems by employing a variable volume balloon with a transparent envelope with a thermal trapping hood. Tockert U.S. Pat. No. 4,986,494 does not employ a semi rigid dirigible having a substantially constant outer surface shape and does not have a cyclical thermal management system for manipulating the temperature of the lifting gas, volume of the lifting gas or the weight of the ballast component. The related prior art does not provide a cyclical thermal management system for reducing skin stress and compensating for diurnal heating and nocturnal cooling or for controlling pitch attitude and providing for the replenishment of lifting gas lost in daily or seasonal cycles that is necessary for providing a long duration high altitude application.
The relevant prior art also includes a variety of passive skin systems for controlling altitude. In Pommereau U.S. Pat. No. 4,361,297 and Sanyo Electric Co. Ltd. Japan Appl. No. 4-26740 the upper part of the skin is transparent while in Graner French 2375-089 a metal foil is disposed between layers to reduce leakage. In, CNES EP-31-981 the lower part of the balloon is transparent. None of these references alone or together provides for a combination of an active and passive system for maintaining a geostatic position.
Related prior art pertaining to manned balloons and dirigibles operating in the troposphere are believed only tangentially relevant due to the extremely different conditions in the stratosphere resulting in differences in processing hydrogen, oxygen and water as well as the utilization of active and passive systems to provide for long duration flights. The helium purification system of Haunschild U.S. Pat. No. 5,090,637 for manned dirigibles and the burning of hydrogen and recovery of water as a by-product of combustion in Fischer U.S. Pat. No. 2,078,532 and Russian U.S. Pat. No. 1,740,250 or the chemical conversion of natural lifting gases in Papst U.S. Pat. No. 3,897,032 are different than the invention as the prior art does not provide for a cyclical thermal management system for stratospheric applications to solve the problem of altitude variations resulting from diurnal heating and nocturnal cooling. Similarly dirigibles having multiple envelopes or layers of skin such as McCampbell U.S. Pat. No. 4,773,617 and the utilization of steam and water vapor to control lift and trim in Papst U.S. Pat. No. 3,456,903 are not particularly pertinent to high altitude applications in the stratosphere. The physical properties of water, steam and their mechanical migration through layers of envelope skin material is very different in the stratosphere than in the troposphere.
The invention provides a cyclical thermal management system for use on stratospheric airships whose application requires they stay aloft in a geostatic position for many months or years. The invention cyclically processes the heat of the lifting gases in response to the heliocyclic stratospheric heating and combines both active and passive measures to control the temperature of the lifting gas and hence the buoyancy of an airship thus enabling it to maintain a constant altitude, pitch attitude and trim in spite of the diurnal heating and nocturnal cooling cycles. Unlike the prior art the duration of the novel high altitude platform in the stratosphere is not limited by the volume of fuel carried by the airship, the volume of lifting gas, the amount of ballast or the energy requirements of the system, but instead the durability of the envelope or skin materials to solar and UV degradation.
The invention does not require terrestrial fuels such as gasoline or diesel oil, nor does it require it to consume its own lifting gas such as hydrogen or methane. Carrying aloft an energy source that does not exist naturally in the stratosphere limits the duration of flight because the airship must land periodically to refuel. Similarly, the invention does not vent lifting gas nor drop non re-acquirable ballast to maintain a constant altitude because lifting gases and ballast materials do not exist naturally in the stratosphere and as a result cannot be replaced, which result in limited flight duration. The invention does not rely on beamed microwave energy from the earth because of questionable environmental consequences and the fact that many applications, such as air traffic control, traffic monitoring or telecommunications, would require the microwave transmission stations to be built in the least feasible areas such as in the heart of major cities or close to the airport.
The invention in the preferred embodiment provides for the utilization of the solar power of the sun, which is an abundant and renewable energy source that is predictably available in the stratosphere as well as albedo flux energy which is always available night and day. Unlike in the troposphere, solar energy is predictably available in the stratosphere unimpeded by moisture or water vapor or clouds. The predictable availability of the sun as well as its predictable seasonal variation in the stratosphere allows the novel cyclical thermal management system to be just as predictably cycled by starting and stopping cyclical heating and cooling processes necessary to counteract the action of the sun in heating and increasing the buoyancy of the lifting gas and the nocturnal cooling of the lifting gas and its resulting decrease in buoyancy. This predictability as well as the seasonal variation allows the starting and stopping of the cyclical thermal management to be no more complicated than utilizing a clock programmed for seasonal variation or using the sun itself to start and stop the novel cyclical thermal management system.
The least predictable variable in the stratosphere is the wind. If the wind changes direction then the airship would have to turn into the wind to remain geostatic. This affects the angle, location and intensity of the sun""s radiant energy across the surface of the airship. If the wind changes velocity, that affects the rate of convection on various areas of the outside surface. Internal temperature variations caused by the winds, combined with intermittent variations in the heat rejection from the on-board equipment, amount to only a few degrees thus allowing the starting and stopping as well as the rate of the cyclical processes to be based upon elapsed time or the duration of sunlight, but the preferred starting and stopping being based on time, pressure and temperature of the lifting gas.
The novel cyclical thermal management of the lifting gas by heating and cooling physical and chemical processes and reactions allows pitch attitude as well as altitude to be controlled by the regulation or thermal manipulation of the lifting gas. The arrangement of the ballonets, system components and payload is designed to maintain a constant trim during the heating and cooling reactions and processes. The novel cyclical thermal management system prevents collected energy from being wasted by using power to drive propellers in combination with wings or elevators in order to maintain a required pitch attitude. The novel cyclical thermal management system allows both pitch attitude and altitude to be controlled without horizontal stabilizers and elevators to impart an overall stability to novel high altitude platforms constructed utilizing the novel cyclical thermal management system.
The invention achieves its advantages by providing a novel cyclical active thermal management system that cyclically manages the heat and hence the buoyancy of the lifting gas in response to the diurnal heating of the buoyant lifting gas by the sun in the stratosphere. The cyclical thermal management of the heat of the lifting gas is achieved by initiating cyclical physical cooling processes to radiate heat from the lifting gas during the day and collecting solar energy during the day and converting it into stored energy to be used at night in conjunction with cyclical physical and chemical heating processes to add heat to the lifting gas during the night to maintain the lifting gas at a relatively constant pressure. Excess collected solar or thermal energy obtained from solar cells or thermionic cells may be stored in batteries or used for propulsion or for the operation of payload equipment. At night a cyclical exothermic process and reaction is initiated to add heat to the lifting gas to maintain the lifting gas at a relatively constant pressure.
The preferred cyclical active system for thermal management of the lifting gases employs cyclical chemical and physical heating and cooling processes and reactions utilizing hydrogen, oxygen and nitrogen since both oxygen and nitrogen are present in the stratosphere and can be vented and later reacquired from the stratosphere as raw materials and subsequently recombined with hydrogen without limiting the duration of the mission of the high altitude platform in the stratosphere. Cyclical reactions involving recyclable hydrogen containing energy storage materials such as water, methanol and other materials containing hydrogen as part of water in a crystal or hydrated form of the material are materials that will be referred to collectively as a hydrogen containing energy storage material. These hydrogen containing energy storage materials and particularly recyclable hydrogen containing energy storage materials can be used not only to store hydrogen combined with another material such as oxygen as ballast for seasonal variations in the daily heating and cooling cycles but also allows hydrogen to be obtained from the ballast and used to replenish a portion of the lifting gases lost as a result of diffusion or in the chemical or thermal manipulation of the,lifting gases. Hydrogen can also be combined with other materials to store lifting gas as ballast until needed for seasonal variations in the diurnal heating and nocturnal cooling cycles.
In the cyclical thermal management of the lifting gas recyclable energy storage materials used for reversible physical and chemical reactions include water, methanol, hydrated, ammoniated or methanolated salts, hydrogenated metals, hydrated zeolites, eutectic salt mixtures, desiccant regeneration cycles using water and phase change compounds capable of storing heat. In the preferred embodiment of the invention, water is disassociated during the day and the heat from the formation of water (+68 Kcal/gmol) plus the heat rejected from the physical process is used to provide exothermic heating of the lifting gas during the night. Similarly, in an alternative embodiment of the invention, methanol is disassociated during the day and the heat from the reformation of methanol (+57 Kcal/gmol) plus the rejected heat from the physical process is used to provide exothermic heating of the lifting gas during the night.
The utilization of cyclical reactions of hydrogen with oxygen, carbon and nitrogen thermal cycles allows hydrogen to be utilized as a lifting gas for replacement of any lifting gases lost through diffusion or repeated cyclical management reactions and to be used by itself as a supplemental lifting gas or stored as water or methanol for seasonal variations. In the preferred embodiment of the invention solar cells or thermionic cells are utilized to collect solar energy and operate an electrolyzer during the day to store energy in the form of hydrogen and oxygen for use at night and to run the compressors and circulating fans required to mitigate the heating effects of the sun during the day. Excess stored energy is stored in a battery or other electrical storage means such as hydrogen and oxygen which can be used to operate a fuel cell to generate heat from exothermic processes or reactions to heat the lifting gas at night.
The cyclical active system which manages the heat of the lifting gas is preferably used in conjunction with other ancillary cyclical active thermal management systems such as variable heat conductance systems such as shutters, louvers and other sensible heat and latent heat systems of the hydrogen containing energy storage material to utilize and manage heat for heating the lifting gas during the night and then reversing some of the physical and chemical processes to cool or reduce the heating of the lifting gas during the day by utilizing latent heat and sensible heat in the hydrogen containing energy storage material. The cyclical active system also includes a novel selectively inflatable envelope or blanket and recyclable energy storage means such as hydrogen and oxygen that can be used to operate a fuel cell to generate heat in envelope of novel high altitude platforms constructed in accordance with the invention. In accordance with the invention the side of the envelope in direct exposure to the sun""s energy is inflated to increase the insulation on this side of the envelope to reduce the heating of the enclosed lifting gas. On the opposite side of the envelope the thermal blanket is deflated to increase the dissipation of heat through the lifting gas and outside the envelope to the shaded side of the high altitude platform where it is radiated into space and convected into the cold atmosphere.
At night the skin is inflated on both sides to insulate the upper half of the high altitude platform to prevent the escape of heat. The cyclical active system also includes fans inside the envelope containing the lifting gas to assist the natural convection currents in maintaining the uniform temperature of the lifting gas.
The cyclical active thermal management system, in the preferred embodiment of the invention is employed with a passive system which reduces the number of heat or energy manipulation steps required to maintain the lifting gas at a constant volume or pressure to control buoyancy. The passive system includes the selection and utilization of varying types of skin materials for the top and bottom of the envelope, reflective coatings on the top side of the high altitude platform to reflect heat and the absence of a reflective coating on the bottom to facilitate absorbing the albedo flux at night to help heat the lifting gas at night and the use of thin reflective coatings, such as aluminum or gold, on the inner layers of the skin or preferably the innermost layer of the skin of the envelope to help maintain a constant pressure of the lifting gas during the day and at night. These passive systems all pertain to the selection of material components to reduce to a minimum the amount of heat manipulations of the lifting gas required by the cyclical active system to maintain the lifting gas at a constant pressure throughout the diurnal heating and nocturnal cooling cycles as well as the seasonal variations of those cycles in relation to a particular geostatic location.
The lifting gas used to provide buoyancy of the high altitude platform may be helium, hydrogen, methane or combinations thereof which are manipulated or processed by the cyclical active system to maintain a geostatic position. Helium and hydrogen and helium and methane combinations are preferred since hydrogen can be utilized to replace lifting gas lost through diffusion and hydrogen can be obtained from the hydrogen containing heat or energy storage material which can act as both an energy storage material and as a ballast material. Hydrogen can alternatively be used to maintain buoyancy or be combined with oxygen and possibly nitrogen that can be obtained from the stratospheric environment and stored or processed in readily accessible compositions to impart lift or reduce lift and to provide flexibility in responding to seasonal variation in the diurnal heating and nocturnal cooling cycles while extending the duration for which the high altitude platform can stay aloft.
The novel cyclical thermal management system contributes to the duration for which a high altitude platform can stay aloft by providing a more efficient and environmentally compatible system for maintaining a high altitude platform in a geostatic position. Instead of having to collect solar energy and then wasting the solar energy on engines, propellers, elevators and other components that become increasingly inefficient and larger with each increase in altitude, the novel thermal management system of the invention provides a more efficient utilization of solar energy to manipulate and regulate the lifting gases to control both altitude and pitch attitude. Unlike the prior art the novel altitude and pitch attitude control provides increasing efficiency in the stratosphere as altitude increases.
The increase of efficiency in the utilization of solar energy provided by the novel cyclical thermal management system allows reduced reliance upon engines and propellers to control altitude and pitch attitude in the stratosphere. As a result most of the power requirements of the propulsion system, engine and propellers can be used to maneuver the high altitude platform for station keeping or counteracting the stratospheric winds at a particular geostatic location. The propulsion systems that may be utilized to propel the high altitude platform from place to place in the stratosphere or to counter the winds aloft can be electric, turbine such as are used on conventional aircraft, hydrogen burning engines or ion engines or other such propulsion devices known in the art. These propulsion systems can also be selected for greatest compatibility with the novel cyclical thermal management system and, where desirable, arranged so that engine heat can be utilized to provide an additional source of heat to counteract the effects of nocturnal cooling and, if desired, for a particular mission utilize excess lifting gas constituents in the form of hydrogen or methane as fuel.